The following invention relates to a paper thickness sensor in a printer.
More particularly, though not exclusively, the invention relates to a paper thickness sensor used for adjusting the space between a printhead and a platen in an A4 pagewidth drop on demand printer capable of printing upto 1600 dpi photographic quality at up to 160 pages per minute.
The overall design of a printer in which the paper thickness sensor can be utilized revolves around the use of replaceable printhead modules in an array approximately 8 inches (20 cm) long. An advantage of such a system is the ability to easily remove and replace any defective modules in a printhead array. This would eliminate having to scrap an entire printhead if only one chip is defective.
A printhead module in such a printer can be comprised of a xe2x80x9cMemjetxe2x80x9d chip, being a chip having mounted thereon a vast number of thermo-actuators in micro-mechanics and micro-electromechanical systems (MEMS). Such actuators might be those as disclosed in U.S. Pat. No. 6,044,646 to the present applicant, however, there might be other MEMS print chips.
The printhead, being the environment within which the paper thickness sensor of the present invention is to be situated, might typically have six ink chambers and be capable of printing four color process (CMYK) as well as infra-red ink and fixative. An air pump would supply filtered air to the printhead, which could be used to keep foreign particles away from its ink nozzles. The printhead module is typically to be connected to a replaceable cassette which contains the ink supply and an air filter.
Each printhead module receives ink via a distribution molding that transfers the ink. Typically, ten modules butt together to form a complete eight inch printhead assembly suitable for printing A4 paper without the need for scanning movement of the printhead across the paper width.
The printheads themselves are modular, so complete eight inch printhead arrays can be configured to form printheads of arbitrary width.
Additionally, a second printhead assembly can be mounted on the opposite side of a paper feed path to enable double-sided high speed printing.
It is an object of the present invention to provide a paper thickness sensor in a printer.
It is another object of the present invention to provide a paper thickness sensor used for adjusting a printhead-to-platen clearance for the pagewidth printhead assembly as broadly described herein.
It is another object of the present invention to provide a pagewidth printhead assembly having a paper thickness sensor therein to aid in adjusting a printhead-to-platen clearance.
It is yet another object of the present invention to provide a method of adjusting the clearance between a printhead and a platen in a pagewidth printhead assembly.
The preset invention provides a pagewidth printer comprising:
a printhead having an array of fixed printing nozzles thereon,
a platen having a platen surface, the platen located opposite the array of fixed printing nozzles;
at least one cam coupled to said platen;
a sensor means arranged to sense a thickness of a print media;
at least one projection fixed relative to said array of fixed printing nozzles and arranged to follow said at least one cam;
means responsive to the sensor means for rotating the at least one cam thereby adjusting the spacing between the fixed array of printing nozzles and the platen by action of the at least one cam upon the at least one projection.
Preferably said platen is mounted so as to rotate about a longitudinal axis thereof and said platen surface extends along the platen parallel with said axis, said pagewidth printer further including a shaft disposed along said axis, wherein the at least one cam is coupled to an end of the shaft.
The platen may include a blotting surface disposed parallel to said axis.
The platen may also include a capping surface disposed parallel to said axis.
In a preferred embodiment the at least one cam is shaped to move the platen away from the fixed array of printing nozzles when transitions between the capping surface, the blotting surface and the platen surface are opposite said nozzles.
Preferably the sensor means includes a pivotal sensor flag that engages the print media.
The sensor means may include an optical sensor that senses movement of the pivotal sensor flag.
In a preferred embodiment the pivotal sensor flag is mounted upon a spring-biased pivotal shaft mounted fixed relative to the printhead.
As used herein, the term xe2x80x9cinkxe2x80x9d is intended to mean any fluid which flows through the printhead to be delivered to a sheet. The fluid may be one of many different coloured inks, infra-red ink, a fixative or the like.